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Abstract
Objectives Knowledge of a study population's similarity to the target population allows researchers to assess the generalisability of their results. Often generalisability is assessed through a comparison of baseline characteristics between individuals who did and did not respond to an invitation to participate in a study. In this prospective population-based cohort, we broadened this assessment by comparing participants with all individuals from a chronic disease register who satisfied the study eligibility criteria but for a number of reasons, such as the absence of consent to be approached for research purposes, did not participate.
Methods Data are from the Living with Diabetes Study, a population-based cohort of individuals diagnosed with diabetes mellitus, which commenced in Queensland, Australia in 2008. Individuals were sampled from a federally-funded diabetes register. We compared the characteristics of 3951 study participants with 10 488 non-participants (individuals who were invited to participate but declined) and with 129 900 non-study individuals on the register who did not participate in the study.
Results Study participants were more likely than non-study registrants to be male, aged 50–69, have type 2 diabetes non-insulin requiring, be recently registered and be non-indigenous Australians. Study participants were more likely than non-participants to be aged 50–69, have type 1 diabetes and be non-indigenous Australians.
Conclusions The interpretation of a study's generalisability can alter depending on which non-participating group is compared with participants. When assessing generalisability, participants should be compared with the largest possible group of non-participating individuals. When sampling from a disease register, researchers should be wary of the influence of research consent procedures on the register's coverage.
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Footnotes
To cite: David M, Ware R, Donald M, et al. Assessing generalisability through the use of disease registers: findings from a diabetes cohort study. BMJ Open 2011;1:e000078. doi:10.1136/bmjopen-2011-000078
Funding This research was funded by the Australian Research Council (DP0988805) and Queensland Health through the Queensland Strategy for Chronic Disease 2005–2015.
Competing interests None.
Ethics approval Ethics approval was provided by The University of Queensland's Behavioural and Social Sciences Ethical Review Committee (BSSERC).
Contributors All authors designed the study. M Donald was responsible for data acquisition. M David and R Ware analysed the data. M David drafted the initial manuscript. R Ware, M Donald and R Alati critically reviewed the manuscript. All authors read and approved the final manuscript.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data used in this study were de-identified (personal identifiers were removed or disguised) before usage. These data are organised and held at the School of Population Health at The University of Queensland. The Living with Diabetes Study's homepage includes information on methodology and study updates including preliminary descriptive findings (www.lwds.org.au). Researchers are invited to contact the research team to explore options for collaborative work.